Adiaphorism, (from Greek adiaphora, “indifferent”), in Christian theology, the opinion that certain doctrines or practices in morals or religion are matters of indifference because they are neither commanded nor forbidden in the Bible. Two adiaphorist controversies occurred in Germany after the Reformation.

The first controversy arose over the religious compromise between the Lutheran theologians of Wittenberg, primarily Philipp Melanchthon, and Saxony’s civil and ecclesiastical leaders. The elector Maurice of Saxony succeeded in making the Wittenberg theologians accept, for political reasons, the Leipzig Interim (December 1548), which sanctioned the jurisdiction of Roman Catholic bishops and observance of certain rites (such as extreme unction and confirmation), while all were to accept the doctrine of justification by faith, the added word “alone” being treated as one of the adiaphora. Matthias Flacius Illyricus, a Lutheran Reformer, passionately opposed this policy on the grounds that under political pressure no adiaphora could be accepted, and, therefore, no concession could be allowed.

In practice the controversy was ended in September 1555 by the Peace of Augsburg, when Lutheranism was acknowledged as a legitimate religion in the empire. The theoretical question of adiaphora, however, continued to be debated by Protestants. The Formula of Concord (1577), a Lutheran confession, attempted to settle the matter by stating that rites and ceremonies that were matters of religious indifference could not be imposed during times of controversy.

Another adiaphorist controversy took place in the field of morality in 1681, when Pietists opposed the construction of a theatre in Hamburg. The Pietists denounced worldly amusements as anti-Christian, whereas Lutherans generally defended Christian freedom in such matters. Although the term “adiaphorism” was not explicitly applied in other disputes, analogous controversies occurred elsewhere. In England the Vestiarian controversy in the 1560s and ’70s dealt with the question of whether clerical vestments—declared to be “popish” by some—were theologically important.